It's simply a dominant chord with an added "flat 5th" tone. Now ... the trick is that you don't play all the tones of the dominant chord. JUST certain tones sound right and I'm going to show you which ones they are below:

In A^b Major:

Bass: There isn't a particular bass for this chord. It can be played over a "running" bass if it is being used as a "fill-in" for shouting music OR ... it can be played in a blues progression. Keep in mind that this chord is just a "fill in." Play it when it "feels" right...

Right hand: A^b + D + E^b + G^b

Note: This chord should be played on the upper part of the piano (not too high but definitely not too low). Test it out at different locations for the best possible sound, ok?

Here's one more trick with the chord above:

If you play the "D" just a split-second before the rest of the chord, it creates a nice "blues" effect. Try it:

A^b + (D) + E^b + G^b

Note: (" ") means to play JUST that one note a split-second before the rest of the chord. It sounds great!